Welcome aboard rajohn78, the HX indicates a 2007 manufacture. It should be a Marlin manufactured barrel with a 1 in 9 twist, if that is the barrel that came with the frame. Check to see if the last 3 numbers of the frame serial number are inscribed on the left side of the barrel lug. You will have to remove the barrel to check for the numbers on the lug. While you have the barrel off the frame it is a simple thing to do to check the twist rate using a cleaning rod and a snug fitting patch. I suggest you do that to be sure. All the info and instrctions you need are in the FAQ's....<><....
